Superprotonic Conductivity of MOFs Confining Zwitterionic Sulfamic Acid as Proton Source and Conducting Medium

A few metal–organic frameworks (MOFs), which typically use strong acids as proton sources, display superprotonic conductivity (≈10−1 S cm−1); however, they are rare due to the instability of MOFs in highly acidic conditions. For the first time, we report superprotonic conductivity using a moderately acidic guest, zwitterionic sulfamic acid (HSA), which is encapsulated in MOF‐808 and MIL‐101. HSA acts not only as a proton source but also as a proton‐conducting medium due to its extensive hydrogen bonding ability and zwitterion effect. A new sustained concentration gradient method results in higher HSA encapsulation compared to conventional methods, producing 10HSA@MOF‐808‐(bSA)2 and 8HSA@MIL‐101. These MOFs show impressive superprotonic conductivity of 2.47×10−1 and 3.06×10−1 S cm−1, respectively, at 85 °C and 98 % relative humidity, and maintain stability for 7 days. Strategic loading of dual‐functioning zwitterionic sulfamic acid in MOFs leads to proton conductivity of the order of 10−1 S cm−1. This high conductivity is the result of higher loading of sulfamic acid, which can act as both a proton source due to its acidity and a conducting medium due to its extensive hydrogen‐bonding ability and zwitterion effect.